Thermoplastic resin compositions containing mixtures of cyclic phosphazenes and phosphoric acid esters

ABSTRACT

The present invention relates to a flame retardant polycarbonate thermoplastic resin composition that comprises a polycarbonate resin, a rubber modified vinyl-grafted copolymer, a phosphorous mixture of a cyclic phosphazene oligomer compound and a phosphoric acid ester as a flame retardant, and a fluorinated polyolefin resin.

FIELD OF THE INVENTION

The present invention relates to a polycarbonate thermoplastic resincomposition with good flame retardancy, heat resistance and mechanicalproperties. More particularly, the present invention relates to a flameretardant polycarbonate thermoplastic resin composition that comprises apolycarbonate resin, a rubber modified vinyl-grafted copolymer, aphosphorous compound mixture of a cyclic phosphazene oligomer compoundand a phosphoric acid ester as a flame retardant, and a fluorinatedpolyolefin resin.

BACKGROUND OF THE INVENTION

A blend of a polycarbonate resin and a styrene-containing copolymer is aresin composition which has improved processability maintaining the goodnotched impact strength. The polycarbonate resin composition shouldfurther have good flame retardancy as well as high mechanical strengthbecause the resin composition are applied to electric or electronicgoods, automobile parts, office supplies, etc.

To provide the polycarbonate resin with good flame retardancy, ahalogen-containing flame retardant and/or an antimony-containingcompound were used. However, the disadvantages could be observed thatthe halogen-containing compound results in the corrosion of the molditself by the hydrogen halide gases released during the molding processand is fatally harmful due to the toxic gases liberated in case of fire.Especially, since the polybromodiphenyl ether, mainly used for ahalogen-containing flame retardant, can produce toxic gases such asdioxin or furan during combustion, flame retardants which are preparedwithout a halogen-containing compound have become a major concern inthis field.

A general method is employ a phosphoric acid ester compound as a flameretardant to provide the polycarbonate resin with flame retardancywithout using a halogen-containing compound. U.S. Pat. No. 4,692,488discloses a thermoplastic resin composition comprising a halogen freearomatic polycarbonate resin, a halogen free SAN (styrene-acrylonitrile)copolymer, halogen free phosphorus compounds as flame retardants, atetrafluoroethylene polymer and a small amount of ABS(acrylonitrile-butadiene-styrene) copolymer. If a halogen freephosphorus compound and a tetrafluoroethylene polymer are used togetheras in this U.S. patent, the dripping phenomenon can be prevented, but ajuicing phenomenon occurs due to the migration of the flame retardantagent to the surface of the molded article during molding process.

U.S. Pat. No. 5,061,745 discloses a thermoplastic resin compositioncomprising an aromatic polycarbonate resin, an ABS graft copolymer, acopolymer, and a monophosphorous ester. As the flame retardant agent ismonomeric, the juicing phenomenon is not prevented and the heatresistance is rapidly deteriorated.

It is known that an oligomeric phosphate is used as a flame retardant.Japanese Patent Publication No. 59-202,240 discloses a method ofpreparing an oligomeric phosphate and the use of the oligomericphosphate in a polyamide or polycarbonate resin composition.

U.S. Pat. No. 5,204,394 discloses a resin composition comprising anaromatic polycarbonate resin, a styrene-containing copolymer or a graftcopolymer, and oligomeric phosphate as flame retardants. Although theresin composition improves the juicing phenomenon and heat resistance,but is inferior to the resin composition using the monophosphorousesters as flame retardants in flame retardancy. Accordingly, to maintaina good flame retardancy, the resin composition should contain more flameretardants than in the resin composition containing monophosphorousester as flame retardants. As a result, the resin composition shows poormechanical properties due to the high content of a flame retardant.Furthermore, the resin composition contains still some monophosphorousester which migrates to the surface of the molded article to causejuicing phenomenon in part.

U.S. Pat. No. 5,672,645 discloses a PC/ABS resin composition comprisingan aromatic polycarbonate resin, a vinyl copolymer, a graft copolymer, amixture of a monophosphate and an oligomeric phosphate, and afluorinated polyolefin. In this case, the resin composition showsjuicing phenomenon in which monophosphorous ester migrates to thesurface of the molded article, and deterioration of heat resistance.And, as the flame retardability of an oligomeric phosphate ester is lessthan that of a momophosphorous ester in usual, the more oligomericphosphate ester is contained in the flame retardant agent, the poorerflame retardancy of resin composition is.

Japanese Patent Laid-open No. 6-100,785 discloses a flame retardantresin composition which comprises a thermoplastic resin, a phosphatecompound, and a silicon resin or a polyphosphazene to prevent fromdripping of the resin during combustion. However, the Japanese patentapplication does not disclose that the flame retardancy of the resincomposition had been improved.

EP 0 728 811 A2 discloses a thermoplastic resin composition comprisingan aromatic polycarbonate, a graft copolymer, a copolymer and aphosphazene. The European patent teaches that no dripping occurs duringcombustion by using a phosphazene as a flame retardant even though anadditional anti-dripping agent is not employed, and that the resincomposition has excellent heat resistance and impact strength. However,the resin composition of the European patent has a poor processabilitydue to the poor flowability by using the phosphazene, and causes blackstripes and/or black lines on the surface of the molded article due todegradation of the resin or flame retardants when an excess stress isapplied to the article during molding. In the European patent usingphosphazene as a flame retardant, mechanical strength such as flexuralstrength and flexural modulus becomes deteriorated, and more amount offlame retardants should be used to maintain a certain degree of flameretardancy.

WO 00/09518 and WO 99/19383 disclose methods of preparing a cross-linkedlinear or cyclic phenoxy phosphazene and a thermoplastic resincomposition using such phosphazene compounds. According to the patentapplications, the cross-linked phenoxy phosphazene does not deterioratethe mechanical properties of the resin composition when applied, becausethe phosphazene has a high melting point and lower volatility. However,the resin composition of the patent applications has a poorprocessability due to the poor flowability by using the phosphazene, andcauses black stripes and/or black lines on the surface of the moldedarticle due to degradation of the resin or flame retardants when anexcess stress is applied to the article during molding. In the patentapplications using phosphazene as a flame retardant, mechanical strengthsuch as flexural strength and flexural modulus becomes deteriorated.

The present inventors have developed a flame retardant thermoplasticresin composition that comprises a polycarbonate resin, a rubbermodified vinyl-grafted copolymer, a vinyl copolymer, an oligomer typecyclic phosphazene compound and a phosphoric acid ester as a flameretardant and a fluorinated polyolefin resin, which has a good balanceof physical properties such as impact strength, heat resistance, heatstability, processability and appearance.

OBJECTS OF THE INVENTION

A feature of the present invention is the provision of an excellentflame retardant thermoplastic resin composition.

Another feature of the present invention is the provision of a flameretardant thermoplastic resin composition with good heat resistance.

A further feature of the present invention is the provision of a flameretardant thermoplastic resin composition with good mechanicalproperties.

A further feature of the present invention is the provision of a flameretardant thermoplastic resin composition with a good balance ofphysical properties such as impact strength, heat stability,processability and appearance.

Other objects and advantages of this invention will be apparent from theensuing disclosure and appended claims.

SUMMARY OF THE INVENTION

A flame retardant thermoplastic resin composition according to thepresent invention comprises (A) about 45 to 95 parts by weight of apolycarbonate resin, (B) about 1 to 50 parts by weight of a rubbermodified vinyl-grafted copolymer prepared by graft-polymerizing (b₁)about 5 to 95 parts by weight of a monomer mixture of about 50 to 95% byweight of styrene, α-methylstyrene, halogen- or alkyl-substitutedstyrene, C₁₋₈ methacrylic acid alkyl ester, C₁₋₈ acrylic acid alkylester, or a mixture thereof and about 5 to 50% by weight ofacrylonitrile, methacrylonitrile, C₁₋₈ methacrylic acid alkyl ester,C₁₋₈ acrylic acid alkyl ester, maleic acid anhydride, C₁₋₄ alkyl- orphenyl N-substituted maleimide or a mixture thereof onto (b₂) about 5 to95 parts by weight of a rubber polymer wherein the rubber polymer isbutadiene rubber, acryl rubber, ethylene-propylene rubber,styrene-butadiene rubber, acrylonitrile-butadiene rubber, isoprenerubber, copolymer of ethylene-propylene-diene (EPDM),polyorganosiloxane-polyalkyl (meth)acrylate rubber or a mixture thereof,(C) about 0 to 50 parts by weight of a vinyl copolymer polymerized with(c₁) about 50 to 95% by weight of styrene, α-methylstyrene, halogen- oralkyl-substituted styrene, C₁₋₈ methacrylic acid alkyl ester, C₁₋₈acrylic acid alkyl ester, or a mixture thereof and (c₂) about 5 to 50%by weight of acrylonitrile, methacrylonitrile, C₁₋₈ methacrylic acidalkyl ester, C₁₋₈ acrylic acid alkyl ester, maleic acid anhydride, C₁₋₄alkyl- or phenyl N-substituted maleimide or a mixture thereof, (D) about1 to 30 parts by weight of a phosphorous mixture of (d₁) about 1 to 50%by weight of a cyclic phosphazene oligomer compound and (d₂) about 99 to50% by weight of a phosphoric acid ester, as a flame retardant, per 100parts by weight of (A)+(B)+(C), and (E) about 0.05 to 5.0 parts byweight of a fluorinated polyolefin resin with average particle size ofabout 0.05 to 1000 μm and density of about 1.2 to 2.3 g/cm³, per 100parts by weight of (A)+(B)+(C).

DETAILED DESCRIPTION OF THE INVENTION

A flame retardant thermoplastic resin composition according to thepresent invention comprises (A) about 45 to 95 parts by weight of apolycarbonate resin, (B) about 1 to 50 parts by weight of a rubbermodified vinyl-grafted copolymer, (C) about 0 to 50 parts by weight of avinyl copolymer, (D) about 1 to 30 parts by weight of a phosphorousmixture of a cyclic phosphazene oligomer compound and a phosphoric acidester, as a flame retardant, per 100 parts by weight of (A)+(B)+(C), and(E) about 0.05 to 5.0 parts by weight of a fluorinated polyolefin resinper 100 parts by weight of (A)+(B)+(C).

Each component will be described in detail as follow:

(A) Polycarbonate Resin

The polycarbonate resin is prepared by reacting a diphenol representedby the following formula (I) with a phosgene, a halogen formate or acarboxylic acid diester:

where A is a single bond, a C₁₋₅ alkylene group, a C₁₋₅ alkylidenegroup, a C₅₋₆ cycloalkylidene group, S or SO₂.

The examples of the diphenol include hydroquinone, resorcinol,4,4′-dihydroxydiphenol, 2,2-bis-(4-hydroxyphenyl)-propane,2,4-bis-(4-hydroxyphenyl)-2-methylbutane,1,1-bis-(4-hydroxyphenyl)-cyclohexane,2,2-bis-(3-chloro-4-hydroxyphenyl)-propane, and2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane. More preferablediphenols are 2,2-bis-(4-hydroxyphenyl)-propane,2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane, and1,1-bis-(4-hydroxyphenyl)-cyclohexane, and the most preferable diphenolis 2,2-bis-(4-hydroxyphenyl)-propane called ‘bisphenol A’.

In the present invention it is preferable that the polycarbonate resin(A) has a weight average molecular weight (M_(w)) of about 10,000 to200,000, more preferably about 15,000 to 80,000.

A polycarbonate with branched chains may also be preferably used. Inparticular a compound with 3 valences or above may be added in an amountof about 0.05 to 2 mol % per the total moles of the diphenol to be used.A homopolymer of polycarbonate, a copolymer of polycarbonate or amixture thereof may be used in this invention. Some portion of thepolycarbonate resin may be replaced with an aromatic polyester-carbonateresin that is obtained by polymerization in the presence of an esterprecursor, such as difunctional carboxylic acid. The polycarbonate resinis used in an amount of about 45 to 95 parts by weight as per 100 partsby weight of the flame retardant thermoplastic resin compositionaccording to the present invention.

(B) Rubber Modified Vinyl-Grafted Copolymer

The rubber modified vinyl-grafted copolymer according to the presentinvention is prepared by graft-polymerizing (b₁) about 5 to 95 parts byweight of a monomer mixture of about 50 to 95% by weight of styrene,α-methylstyrene, halogen- or alkyl-substituted styrene, C₁₋₈ methacrylicacid alkyl ester, C₁₋₈ acrylic acid alkyl ester, or a mixture thereofand about 5 to 50% by weight of acrylonitrile, methacrylonitrile, C₈methacrylic acid alkyl ester, C₁₋₈ acrylic acid alkyl ester, maleic acidanhydride, C₁₋₄ alkyl- or phenyl N-substituted maleimide or a mixturethereof onto (b₂) about 5 to 95 parts by weight of a rubber polymerwherein the rubber polymer is butadiene rubber, acryl rubber,ethylene-propylene rubber, styrene-butadiene rubber,acrylonitrile-butadiene rubber, isoprene rubber, copolymer ofethylene-propylene-diene (FPDM),polyorganosiloxane-polyalkyl(meth)acrylate rubber or a mixture thereof.

The C₁₋₈ methacrylic acid alkyl ester is obtained from methacrylic acidand monohydric alcohol with 1 to 8 carbon atoms and the C₁₋₈ acrylicacid alkyl ester from acrylic acid and monohydric alcohol with 1 to 8carbon atoms. The examples of the acid alkyl ester include methacrylicacid methyl ester, methacrylic acid ethyl ester, acrylic acid methylester, acrylic acid ethyl ester, and methacrylic acid propyl ester.Methacrylic acid methyl ester is the most preferable.

Preferable examples of the rubber modified vinyl-grafted copolymer aregrafted-polymers obtained by graft polymerizing a mixture of styrene andacrylonitrile, and, optionally, (meth)acrylic acid alkyl ester ontobutadiene rubber, acryl rubber or styrene-butadiene rubber, or by graftpolymerizing (meth)acrylic acid alkyl ester onto butadiene rubber, acrylrubber or styrene-butadiene rubber. The most preferable examples of therubber modified vinyl-grafted copolymer are a grafted-polymer that amixture of styrene and acrylonitrile is grafted onto butadiene rubber,which is called acrylonitrile-butadiene-styrene (ABS) resin, and agrafted-polymer of MBS resin.

The rubber polymer to prepare the rubber modified vinyl-graftedcopolymer has preferably an average particle size of about 0.05 to 4.0μm considering the impact strength and appearance.

The rubber modified graft copolymer according to the present inventioncan be prepared through a conventional polymerization process such asemulsion, suspension, solution or bulk process. However, the copolymercan be preferably prepared through the emulsion or bulk process in whichvinyl monomers are added to the rubber polymer using an initiator.

The rubber modified vinyl-grafted copolymer is used in an amount ofabout 1 to 50 parts by weight as per 100 parts by weight of the flameretardant thermoplastic resin composition according to the presentinvention.

(C) Vinyl Copolymer

The vinyl copolymer of the present invention is a copolymer that ispolymerized with (c₁) about 50 to 95% by weight of styrene,α-methylstyrene, halogen- or alkyl-substituted styrene, C₁₋₈ methacrylicacid alkyl ester, C₁₋₈ acrylic acid alkyl ester, or a mixture thereofand (c₂) about 5 to 50% by weight of acrylonitrile, methacrylonitrile,C₁₋₈ methacrylic acid alkyl ester, C₁₋₈ acrylic acid alkyl ester, maleicacid anhydride, C₁₋₄ alkyl- or phenyl N-substituted maleimide or amixture thereof. A mixture of the copolymers may be used as thecomponent (C).

The C₁₋₈ methacrylic acid alkyl ester is obtained from methacrylic acidand monohydric alcohol with 1 to 8 carbon atoms and the C₁₋₈ acrylicacid alkyl ester from acrylic acid and monohydric alcohol with 1 to 8carbon atoms. The examples of the acid alkyl ester include methacrylicacid methyl ester, methacrylic acid ethyl ester, acrylic acid methylester, acrylic acid ethyl ester, and methacrylic acid propyl ester.Methacrylic acid methyl ester is the most preferable.

The vinyl copolymer can be produced as by-products when preparing therubber modified vinyl-grafted copolymer (B). The by-products are mostlyproduced when an excess of monomers are grafted onto a small amount ofrubber polymer or when a chain transfer agent is used in excess. Theamount of the vinyl copolymer to be used in this invention does notinclude the amount of the by-products that might be produced duringpreparation of the rubber modified vinyl-grafted copolymer (B).

The preferable examples of the vinyl copolymer are a copolymer ofstyrene and acrylonitrile, a copolymer of α-methylstyrene andacrylonitrile, and a copolymer of styrene, α-methylstyrene andacrylonitrile. The vinyl copolymer is preferably prepared by emulsion,suspension, solution or bulk process, and has a weight average molecularweight (M_(w)) of about 15,000 to 200,000.

Another preferable examples of the vinyl copolymer (C) is a copolymerprepared from a mixture of methacrylic acid methyl ester monomers andoptionally acrylic acid methyl ester monomers. The vinyl copolymer ispreferably prepared by emulsion, suspension, solution or bulk process,and has a weight average molecular weight (M_(w)) of about 20,000 to250,000.

A further preferable example of the vinyl copolymer is a copolymer ofstyrene and maleic acid anhydride, which is prepared by a continuousbulk process or a solution process. The maleic acid anhydride ispreferably used in the amount of about 5 to 50% by weight. The copolymerof styrene and maleic acid anhydride has a weight average molecularweight (M_(w)) of about 20,000 to 200,000 and an intrinsic viscosity ofabout 0.3 to 0.9.

The styrene for preparation of the component (C) in this invention canbe replaced with p-methylstyrene, vinyltoluene, 2,4-dimethylstyrene orα-methylstyrene.

The vinyl copolymer is used in an amount of about 0 to 50 parts byweight as per 100 parts by weight of the flame retardant thermoplasticresin composition according to the present invention.

(D) Phosphorous Mixture of Cyclic Phosphazene Oligomer and PhosphoricAcid Ester

(D₁) Cyclic Phosphazene Oligomer

The cyclic phosphazene oligomer according to the present invention is anoligomer type compound or their mixture of the cyclic phosphazene linkedwith a linking group having a R₂ group, which is represented asfollowing Formula (II):

where R₁ is alkyl, aryl, alkyl substituted aryl, aralkyl, alkoxy,aryloxy, amino or hydroxyl, k and m are an integer from 1 to 10, R₂ isdioxyarylene group of C₆₋₃₀ or a derivative thereof, and n is 0 or aninteger representing the number of repeating unit and the average valueof n in the mixture of the compound is 0.3 to 3. The alkoxy and aryloxygroups may be substituted with alkyl, aryl, amino, hydroxyl etc.

In Formula (II), when cyclic phosphazenes of n+1 monomers are linked,the oligomer of cyclic phosphazene is obtained, which has a numberaverage degree of polymerization of n.

It is preferable that the mixture of cyclic phosphazene oligomer has anumber average degree of polymerization (n) of 0.3 to 3. In the presentinvention, cyclic phosphazene oligomers having n value of 0 to 10 may bepreferably used in single or in combination as a mixture. The cyclicphosphazene oligomers may be mixed before or after polymerization. Thecyclic phosphazene oligomers may have a branched chain.

In Formula (II), the more preferable groups of R₁ are alkoxy andaryloxy, and the most preferable groups of R₁ is phenoxy.

The preferable group of R₂ is a derivative from catechol, resorcinol,hydroquinone, or the bisphenylenediol of the following Formula (III):

where Y is alkylene of C₁₋₅, alkylidene of C₁₋₅, cycloalkylidene ofC₅₋₆, S or SO₂, and z is 0 or 1.

The cyclic phosphazene oligomer of the present invention can be preparedthrough a conventional method which is not limited. The following methodfor preparation can be appropriately adopted.

Allyl alcohol or aryl alcohol reacts with alkali metal hydroxide such assodium hydroxide and lithium hydroxide to prepare alkali metal alkylateor alkali metal arylate. In the same manner, diol with R₂ group reactswith alkali metal hydroxide to prepare alkali metal diarylate. Cyclicdichlorophophazene reacts with a mixture of the alkali metal alkylate oralkali metal arylate and the alkali metal diarylate, and the resultingsolution reacts further with the alkali metal alkylate or alkali metalarylate to obtain the cyclic phosphazene oligomer according to thepresent invention.

(D₂) Phosphoric Acid Ester

The phosphoric acid ester is represented by the following Formula (IV).The phosphoric acid ester may be used in single or in combination as amixture.

where R₃, R₄, R₅ and R₇ are a C₆₋₂₀ aryl group or an alkyl-substitutedC₆₋₂₀ aryl group, respectively, preferably a phenyl group or analkyl-substituted phenyl group in which alkyl is methyl, ethyl,isopropyl, t-butyl, isobutyl, isoamyl or t-amyl, preferably methyl,ethyl, isopropyl or t-butyl; R₅ is a C₆₋₃₀ arylene group or analkyl-substituted C₆₋₃₀ arylene group, preferably resorcinol,hydroquinone or bisphenol-A; and l means the number of repeating unitsand the average value of l in the phosphate mixture is 0 to 3.

In the present invention, it is preferable to use an oligomer typephosphoric acid ester that is a derived from a C₆₋₃₀ arylene group andhas an average value of l of about 0 to 3. The oligomer type phosphoricacid ester is a mixture of oligomers in which l is 0, 1, 2 and 3,respectively. The oligomer type phosphoric acid esters are mixed beforeor after polymerization.

The representative examples of the phosphoric acid ester with l=0 aretri(alkylphenyl)phosphate, di(alkylphenyl)monophenylphosphate,diphenylmono(alkylphenyl)phosphate and triphenylphosphate. Thephosphoric acid ester can be used in single or in combination as amixture.

About 1 to 30 parts by weight of a phosphorous mixture of (d₁) about 1to 50% by weight of a cyclic phosphazene oligomer compound and (d₂)about 99 to 50% by weight of a phosphoric acid ester, as a flameretardant, per 100 parts by weight of (A)+(B)+(C).

(E) Fluorinated Polyolefin Resin

The fluorinated polyolefin resin (E) according to the present inventionis prepared by a conventional process, for example, the resin isprepared in an aqueous solvent at 7˜71 kg/cm² and 0˜200° C., preferably20˜100° C., in the presence of a free radical forming catalyst such assodium-, potassium-, or ammonium-peroxydisulphate.

The examples of the fluorinated polyolefin resin arepolytetrafluoroethylene, polyvinylidenefluoride,tetrafluoroethylene/vinylidenefluoride copolymer,tetrafluoroethylene/hexafluoropropylene copolymer, andethylene/tetrafluoroethylene copolymer. The fluorinated polyolefin resinmay be used in single or in combination as a mixture. The fluorinatedpolyolefin resin has preferably average particle size of about 0.05 to1000 μm and density of about 1.2 to 2.3 g/cm³.

The fluorinated polyolefin resin functions to form a fibrillar networkwhen the resin composition containing the fluorinated polyolefin resinis extruded, resulting to increase the flow viscosity and to increasethe shrinkage during combustion so as to prevent the dripping phenomena.

The fluorinated polyolefin resin is used in emulsion state or in powderstate. In case using in emulsion state, dispersion of the fluorinatedpolyolefin resin is good, but the process will be somewhat complicated.Accordingly, if the fluorinated polyolefin resin could be uniformlydispersed in the entire resin composition to form the fibrillar networkstructure, it is preferable to use the fluorinated polyolefin resin inpowder state.

The fluorinated polyolefin resin is used in an amount of about 0.05 to5.0 parts by weight as per 100 parts by weight of (A)+(B)+(C) of theflame retardant thermoplastic resin composition according to the presentinvention.

Other additives may be contained in the resin composition of the presentinvention. The additives include an additional flame retardant, alubricant, a releasing agent, an anti-dripping agent, an impactmodifier, a plasticizer, a heat stabilizer, an oxidation inhibitor, alight stabilizer, a compatibilizer and the like. An inorganic fillersuch as talc, silica, mica, glass fiber, an organic or inorganic pigmentand/or dye can be added too. The additives are employed in an amount ofabout 0 to 60 parts by weight as per 100 parts by weight of (A)+(B)+(C)of the flame retardant thermoplastic resin composition, preferably about1 to 40 parts by weight.

The flame retardant thermoplastic resin composition according to thepresent invention can be prepared by a conventional method. All thecomponents and additives are mixed together and extruded through anextruder and are prepared in the form of pellets.

The flame retardant thermoplastic resin composition according to thepresent invention can be applied to electric or electronic goods,automobile parts, office supplies, etc which require good flameretardancy, weld-line strength and impact strength.

The invention may be better understood by reference to the followingexamples which are intended for the purpose of illustration and are notto be construed as in any way limiting the scope of the presentinvention, which is defined in the claims appended hereto. In thefollowing examples, all parts and percentage are by weight unlessotherwise indicated.

EXAMPLES

The components to prepare flameproof thermoplastic resin compositions inExamples 1˜6 and Comparative Examples 1˜7 are as follows:

(A) Polycarbonate Resin

Bisphenol-A with a weight average molecular weight (M_(w)) of about25,000 was used as polycarbonate resin.

(B) Rubber Modified Vinyl-Grafted Copolymer

(B₁) 50 parts of butadiene rubber latex, 36 parts of styrene, 14 partsof acrylonitrile and 150 parts of deionized water were mixed. To themixture, 1.0 parts of potassium oleate, 0.4 parts of cumenhydroperoxide,and 0.3 parts of t-dodecyl mercaptan chain transfer agent were added.The blend was kept at 75° C. for 5 hours to obtain ABS latex. To the ABSlatex, 1% sulfuric acid was added, coagulated and dried to obtainstyrene-containing graft copolymer resin (g-ABS) in powder form.

(B₂) A graft copolymer of EXL-2602 (product name) by Kureha Co. wasused, in which methacrylic acid ester monomers are grafted ontobutadiene rubber.

(C) Vinyl Copolymer

71 parts of styrene, 29 parts of acrylonitrile, 120 parts of deionizedwater and 0.2 parts of azobisisobutylonitrile (AIBN) were blended. Tothe blend, 0.5 parts of tricalciumphosphate and 0.3 parts ofmercaptan-containing chain transfer agent were added. The resultantsolution was heated to 80° C. for 90 minutes and kept for 180 minutes.The resultant was washed, dehydrated and dried. Styrene-acrylonitrilecopolymer (SAN) was obtained.

(D) Phosphorous Compound

(d₁) Cyclic Phosphazene Oligomer

The cyclic phosphazene oligomer is a mixture of: 66.5% by weight of anoligomer of Formula (II) in which R₁ is phenoxy, k and m are 1 or 2, andn is 0; 20.3% by weight of an oligomer of Formula (II) in which R₁ isphenoxy, R₂ is a derivative from resorcinol, k and m are 1 or 2, and nis 1; 4.9% by weight of an oligomer of Formula (U) in which R₁ isphenoxy, R₂ is a derivative from resorcinol, k and m are 1 or 2, and nis 2; and 8.3% by weight of an oligomer of Formula (II) in which R₁ isphenoxy, R₂ is a derivative from resorcinol, k and m are 1 or 2, and nis 3 or more.

(d₂) Phosphate Compound

(d_(2a)) The bisphenol-A type phosphoric acid ester represented by thechemical Formula (IV) is used, where R₃, R₄, R₆ and R₇ are a phenylgroup, which consists of 3.4% by weight of the compound of l=0, 85.4% byweight of the compound of l=1, and 11.1% by weight of the compound ofl=2, and which has an average of l=1.0. The phosphoric acid ester ismanufactured by Daihachi Co. of Japan as CR-741S (product name).

(d_(2b)) Triphenylphosphate (TPP) of 1=0 in the chemical Formula(IV) wasused. The TPP is manufactured by Daihachi Co. of Japan.

(d₃) Linear Cross-linked Phosphazene.

The phosphazene used in the Comparative Examples is a mixture of linearcross-linked phosphazene oligomers. The mixture was prepared to link 62%by weight of phenoxy phosphazene trimer, 12% by weight of phenoxyphosphazene tetramer, and 26% by weight of phenoxy phosphazene pentameror more with hydroquinone. The molar ratio of phenoxy to hydroquinone is1.7 to 0.15 and the weight average molecular weight is about 1100.

(E) Fluorinated Polyolefin Resin

Teflon (registered trademark) 7AJ by Dupont company was used.

Examples 1–6

The components as shown in Table 1, an antioxidant and a heat stabilizerwere mixed in a conventional mixer and the mixture was extruded througha twin screw extruder with L/D=35 and Ø=45 mm at 240° C. to prepare inpellet form. The resin pellets were molded into test specimens formeasuring flame retardancy and mechanical properties using a 10 ozinjection molding machine at 240° C. The specimens were kept at therelative humidity of 50% at 23° C. for 48 hours. The physical propertieswere measured in accordance with ASTM regulations.

Comparative Examples 1–7

Comparative Example 1 was conducted in the same manner as in Example 1except that the phosphorous mixture with different composition was usedas in Table 1.

Comparative Examples 2–4 were conducted in the same manner as in Example1 except that a single phosphorous compound was used as in Table 1.

Comparative Example 5 was conducted in the same manner as in Example 2except that a linear phosphazene oligomer was used as in Table 1.

Comparative Example 6 was conducted in the same manner as in Example 6except that a phosphorous acid ester compound only was used as in Table1.

Comparative Example 7 was conducted in the same manner as in Example 6except that a linear phosphazene oligomer was used as in Table 1.

TABLE 1 Examples Comparative Examples 1 2 3 4 5 6 1 2 3 4 5 6 7 (A) 7575 75 75 75 95 75 75 75 75 75 95 95 (B) (B₁) 12 12 12 12 12 — 12 12 1212 12 — — (B₂) — — — — — 5 — — — — — 5 5 (C) 13 13 13 13 13 — 13 13 1313 13 — — (D) (d₁) 1 3 5 2 2 1 10 13 — — — — — (d_(2a)) 10 8 7 11 — 2 2— 13 — 8 3 2 (d_(2b)) 2 2 1 — 11 1 1 — — 13 2 1 1 (d₃) — — — — — — — — —— 3 — 1 (E) 0.5 0.5 0.5 0.5 0.5 0.4 0.5 0.5 0.5 0.5 0.5 0.4 0.4

The mechanical properties of the test specimens of Examples 1–6 andComparative Examples 1–7 were measured as follow:

(1) Flame Retardancy

The flame retardancy was measured in accordance with UL94VB. The testspecimens have a thickness of 1.6 mm.

(2) Total Flame Out Time

For each Example, five specimens were tested twice. The total flame outtime is the sum of the first flame out time and the second flame outtime.

(3) Flexural Strength

The flexural strength was measured in accordance with ASTM D790.

(4) Heat Distortion Temperature

The heat distortion temperature was measured in accordance with ASTMD648 under 18.6 kgf.

(5) Melt Flow Index

The melt flow index was measured in accordance with ASTM D1238 under220° C./10 kgf.

The test results of Examples 1–6 and Comparative Examples 1–7 are shownin Table 2.

TABLE 2 Examples Comparative Examples 1 2 3 4 5 6 1 2 3 4 5 6 7 UL94VB(1/16″) V-0 V-0 V-0 V-0 V-0 V-0 V-1 V-1 V-2 V-1 V-1 V-1 V-1 Total FlameOut 18 20 21 22 12 13 68 75 124 55 67 66 64 Time (sec) Flexural 835 850  845  840  845  910  820  805  820  825  830  895  900  Strength HDT85 85 88 90 84 120  91 95 86 80 84 119  120  MFI 39 36 34 34 40 20 30 2537 42 36 22 21

As shown in Table 2, the resin compositions employing a phosphorousmixture of cyclic phosphazene oligomer and phosphorous acid ester showsynergistic effect in flame retardancy and flexural strength with no bigdifference in heat distortion temperature and melt flow index, comparedto those employing a single phosphorous compound. The resin compositionusing a linear phosphazene oligomer shows a poor flame retardancy.

The present invention can be easily carried out by an ordinary skilledperson in the art. Many modifications and changes may be deemed to bewith the scope of the present invention as defined in the followingclaims.

1. A flame retardant thermoplastic resin composition comprising: (A)about 45 to 95 parts by weight of a polycarbonate resin; (B) about 1 to50 parts by weight of a rubber modified vinyl-grafted copolymer preparedby graft-polymerizing (b₁) about 5 to 95 parts by weight of a monomermixture of about 50 to 95% by weight of at least one of styrene,α-methylstyrene, halogen-substituted styrene, alkyl-substituted styrene,C₁₋₈ methacrylic acid alkyl ester, C₁₋₈ acrylic acid alkyl ester, or amixture thereof and about 5 to 50% by weight of acrylonitrile,methacrylonitrile, C₁₋₈ methacrylic acid alkyl ester, C₁₋₈ acrylic acidalkyl ester, maleic acid anhydride, or C₁₋₄ alkyl- or phenylN-substituted malcimide onto (b₂) about 5 to 95 parts by weight of arubber polymer wherein the rubber polymer is butadiene rubber, acrylrubber, ethylene-propylene rubber, styrene-butadiene rubber,acrylonitrile-butadiene rubber, isoprene rubber, copolymer ofethylene-propylene-diene (FPDM), polyorganosiloxane-polyalkyl(meth)acrylate rubber or a mixture thereof; (C) about 0 to 50 parts byweight of a vinyl copolymer polymerized with (c₁) about 50 to 95% byweight of at least one of styrene, α-methylstyrene, halogen- oralkyl-substituted styrene, C₁₋₈ methacrylic acid alkyl ester, or C₁₋₈acrylic acid alkyl ester and (c₂) about 5 to 50% by weight of at leastone of acrylonitrile, methacrylonitrile, C₁₋₈ methacrylic acid alkylester, C₁₋₈ acrylic acid alkyl ester, maleic acid anhydride, and C₁₋₄alkyl-maleimide or phenyl N-substituted maleimide; (D) about 1 to 30parts by weight of a phosphorous mixture, as a flame retardant, per 100parts by weight of (A)+(B)+(C), of (d₁) about 1 to 50% by weight of acyclic phosphazene represented by the following formula;

where R₁ is alkyl, aryl, alkyl substituted aryl, aralkyl, alkoxy,aryloxy, amino or hydroxyl, k and m are an integer from 1 to 10, R₂ isdioxyarylene group of C₆₋₃₀ or a derivative thereof, and n is 0 or aninteger representing the number of repeating unit and the average valueof n in the mixture of the phosphazene compound is 0.3 to 3; and (d₂)about 99 to 50% by weight of a phosphoric acid ester represented by thefollowing formula;

where R₃, R₄, R₆ and R₇ are a C₆₋₂₀ aryl group or an alkyl-substitutedC₆₋₂₀ aryl group, respectively; R₅ is a C₆₋₃₀ arylene group or analkyl-substituted C₆₋₃₀ arylene group; and l means the number ofrepeating unit and the average value of l in the phosphate mixture is 0to 3; and (F) about 0.05 to 5.0 parts by weight of a fluorinatedpolyolefin resin with average particle size of about 0.05 to 1000 μm anddensity of about 1.2 to 2.3 g/cm³, per 100 parts by weight of(A)+(B)+(C).
 2. The flame retardant thermoplastic resin composition asdefined in claim 1, wherein said cyclic phosphazene has a linearstructure or a structure with a branched chain at the main chain.
 3. Theflame retardant thermoplastic resin composition as defined in claim 1,wherein R₁ is phenoxy and R₂ is a derivative from catechol, resorcinol,hydroquinone, or the bisphenylenediol represented by the followingformula:

where Y is alkylene of C₁₋₅, alkylidene of C₁₋₅, cycloalkylidene ofC₅₋₆, S or SO₂, and z is 0 or
 1. 4. The flame retardant thermoplasticresin composition as defined in claim 1, wherein said R₃, R₄, R₆ and R₇are a phenyl group or an alkyl-substituted phenyl group where the alkylis selected from the group consisting of methyl, ethyl, isopropyl andt-butyl, and R₅ is a derivative from resorcinol, hydroquinone, orbisphenol-A.
 5. A molded article produced from the flame retardantthermoplastic resin composition as defined in claim
 1. 6. The flameretardant thermoplastic resin composition as defined in claim 1, whereinsaid R₃, R₄, R₆ and R₇ are a phenyl group or an alkyl-substituted phenylgroup where the alkyl is methyl, ethyl, isopropyl or t-butyl.
 7. Theflame retardant thermoplastic resin composition as defined in claim 6,wherein said R₃, R₄, R₆ and R₇ are an alkyl-substituted phenyl groupwhere the alkyl is methyl, ethyl, isopropyl or t-butyl.
 8. The flameretardant thermoplastic resin composition as defined in claim 1, whereinR₅ is a derivative from resorcinol, hydroquinone, or bisphenol-A.
 9. Amolded article produced from the flame retardant thermoplastic resincomposition as defined in claim
 2. 10. A molded article produced fromthe flame retardant thermoplastic resin composition as defined in claim3.
 11. A molded article produced from the flame retardant thermoplasticresin composition as defined in claim 4.